Frame geometry - understanding how it will ride

Wrath Rob

So, I'm currently in the process of getting a custom frame made. Something British in titanium that should be a forever bike that meets my commuting and winter requirements. And that runs disc brakes .

I've got to the stage of picking a frame builder, ridden a few off the peg bikes, selected the style I want and the features and I now have an engineers drawing of the proposed frame. The problem I've got is that I'm not sure how to convert the on-paper drawing and measurements into how the bike will ride. Anyone got any experience they could lend?

jejv

How tall are you ?
IMO, wheelbase should somewhat scale with your height. For comfort & static stability.
A long wheelbase need not compromise sideways rigidity, because the chainstay bridge can move back with the tyre, and the space between the chainstay bridge and the BB can be braced.
http://yarchive.net/bike/frame_dimensions.html

Anyway, post some pics of what you end up with. I'm sure you'll love it.

cjcp

Rob - out of interest, why would you want to deviate from your present geometry?

Fwiw, I tend to stick to a 56cm top tube, then play around with (i) stem length, (ii) seatpost height, (iii) saddle* height, and (iv) hood positioning.

*why is it not a seat height, or a saddle post? Anyway...

clarkey cat

WR - perhaps you should drop Hoopdriver a line. He had a pretty impressive "forever bike" build put together by Enigma IIRC and he seemed to know exactly what he was after.

styxd

Go for some short chainstays, they ride loads better!

Thats all I know.

kieranb

Have you had a chat with the frame builder? Surely they should be able to help.

tgotb

Seat tube angle
More upright for a weight-forward, low front end, aero position
Less upright for a more relaxing, higher front end, less aero position with less weight on your hands
Think of a TT bike at one extreme (tip of saddle above bottom bracket), and something like a Pashley at the opposite end. To a limited extent you can move the saddle forward/back to achieve the same effect.

Head tube length
Fairly obvious, but should be related to the seat tube angle (TT bikes tend to have short head tubes). To a limited extent you can raise /lower the stem height.

Head tube angle
Has a big effect on the handling. More upright seems to gives you better manoeuvrability and less directional stability, and more rake (that may be the wrong term) does the opposite.
The fork geometry is pretty significant here (how far the front axle is ahead of the line of the head tube) but I've never been able to get my head around how these interact. Stem length also has an impact on handling, which is why using a very long/short stem to compensate for having the wrong frame size is generally not a great idea.

Wrath Rob

cjcp wrote:

Rob - out of interest, why would you want to deviate from your present geometry?

Fwiw, I tend to stick to a 56cm top tube, then play around with (i) stem length, (ii) seatpost height, (iii) saddle* height, and (iv) hood positioning.

*why is it not a seat height, or a saddle post? Anyway...

I suppose I should have explained myself a little better! From this bike I want a few things. First, to have a bike that meets my requirements, i.e. a road geometry bike with disc brakes, mounts for mudguards and clearance for up to 28mm tyres in titanium that is suitable for winter riding and commuting. Everything else I've seen out there is either a compromise (CX bikes) or incredibly expensive (Clagno C59) or not titanium (Volagi). I want Ti for its supple ride and last-a-lifetime abilities. Also, by customising the geometry I should be able to have the ride properties I want. For example I tried their off-the-peg road bike and it was a lovely, smooth ride but had an enormous head tube, where as their race bike was much faster but had a teeny head tube that would have put a crick in my neck. Something between the 2 is where I want to go.

Second, for it to fit me rather than an off-the-peg, close to me fit that then relies on some tweaks. When I had my bike fit it became clear that my body put me outside of the normal range and therefore away from standard bike sizes. I can make a bike fit me but this results in a compromise position that while comfortable, is not necessarily ideal. For example, the Fuji has been made to fit me well through the use of a seat post with a large amount of set back, plus a saddle with long rails and a short stem. By tailoring the geometry I can eliminate the needs for such extreme measures. For example, I probably need to go to the next size stem down, but this would make the handling pretty twitchy and I'm already annoyed that my Garmin has moved to my 'bars!

Finally, I can make this a distinct and unique bike. The company offer different tubing and I can use this to ensure I get something completely one off. I'll also try and add some personal touches to the bike too so it will always be my bike.

il_principe

Wrath Rob wrote:

So, I'm currently in the process of getting a custom frame made. Something British in titanium that should be a forever bike that meets my commuting and winter requirements. And that runs disc brakes .

I've got to the stage of picking a frame builder, ridden a few off the peg bikes, selected the style I want and the features and I now have an engineers drawing of the proposed frame. The problem I've got is that I'm not sure how to convert the on-paper drawing and measurements into how the bike will ride. Anyone got any experience they could lend?

If you must have disc brakes, prob best to go Hydraulic.

http://velonews.competitor.com/2012/08/bikes-and-tech/technical-faq/technical-faq-throwing-ice-water-on-road-disc-brakes_235280

MichaelW

How tall are you?
If you are medium sized, then the std geometries of bikes are well known and work well.
If you are tall or short, then the std geometries used in off-the-shelf bikes are not very good and you can use custom build to fix the issues.

Read "Touring Bikes: A Practical Guide" by Tony Oliver, the best discussion of how bike geometry affects handling, dealing with race, Audax, touring and rigid MTB styles.

Hydraulic brakes would be nice but where do you get a brake lever from? The cable-hydro converter is just a temporary hack until SRAM get their act together and make a hydro road groupset.
Take note where you place the rear brake to avid conflict with rack and mudguard stays

styxd

I want Ti for its supple ride and last-a-lifetime abilities

Nah, you want steel for that.

il_principe

Which builder have you gone for? I'd love to have Feather build me something one day, this os rather beautiful:

Paul E

styxd wrote:

I want Ti for its supple ride and last-a-lifetime abilities

Nah, you want steel for that.

Steel won't last as long as Ti though as it's for a forever bike

UndercoverElephant

Paul E wrote:

styxd wrote:

I want Ti for its supple ride and last-a-lifetime abilities

Nah, you want steel for that.

Steel won't last as long as Ti though as it's for a forever bike

Steel may corrode more than Ti, but the welds on steel will last a whole lot longer unless the frame builder is absolutely top-class.

pangolin

There are a couple of interesting threads here with some first hand experience of Ti frames cracking.

Sorry for cross forum link! They are very worth a read though

http://yacf.co.uk/forum/index.php?topic=62132.0

http://yacf.co.uk/forum/index.php?topic=62367.0

The Rookie

The only relevant bits are
1/ Head tube height, go a fraction short (10mm) and you can always add a spacer if you want
2/ EFFECTIVE top tube length, horizontal distance from head tube to seat tube
3/ Seat tube angle
Noting you can tweak the effective 2 and 3 with a layback versus inline seatpost and also by moving saddle a little on the runners, so once you think you know what you want for 2 have it made so its the midpoint between saddle right forward on an inline and right back on a set back, likewise seat tube angle.

styxd

Paul E wrote:

styxd wrote:

I want Ti for its supple ride and last-a-lifetime abilities

Nah, you want steel for that.

Steel won't last as long as Ti though as it's for a forever bike

A forever bike?

Stop deluding yourself, look at all the cracked Ti frames. Then once they're broken, who's going to fix them?

Steel is fine, Im sure if you left it at the bottom of the sea bed it would rust after hundreds of years, but msot people tend to keep their bikes in the hosue or the shed.

Get some stainless stuff if you're that worried.

Steel is stronger and is easier to repair if it does go wrong.

Paul E

Sorry if I came across as deluded

rjsterry

styxd wrote:

Paul E wrote:

styxd wrote:

I want Ti for its supple ride and last-a-lifetime abilities

Nah, you want steel for that.

Steel won't last as long as Ti though as it's for a forever bike

A forever bike?

Stop deluding yourself, look at all the cracked Ti frames. Then once they're broken, who's going to fix them?

Steel is fine, Im sure if you left it at the bottom of the sea bed it would rust after hundreds of years, but msot people tend to keep their bikes in the hosue or the shed.

Get some stainless stuff if you're that worried.

Steel is stronger and is easier to repair if it does go wrong.

I'd heard that some of the high-end "stainless" steels were actually pretty difficult to weld, but yes, assuming even a basic level of care and maintenance, a rust isn't a problem on the frame. Also, steel can crack too as UndercoverElephant's will testify.

UndercoverElephant

rjsterry wrote:

I'd heard that some of the high-end "stainless" steels were actually pretty difficult to weld, but yes, assuming even a basic level of care and maintenance, a rust isn't a problem on the frame. Also, steel can crack too as UndercoverElephant's will testify.

He's right, you know:



There wasn't any perceivable rust anywhere in that area of the frame either. If it had been a better frame, it would have been off to Bob Jackson's for a downtube transplant, that would be much harder to do on Ti.

tgotb

The Beginner wrote:

The only relevant bits are1/ Head tube height, go a fraction short (10mm) and you can always add a spacer if you want
2/ EFFECTIVE top tube length, horizontal distance from head tube to seat tube
3/ Seat tube angle
Noting you can tweak the effective 2 and 3 with a layback versus inline seatpost and also by moving saddle a little on the runners, so once you think you know what you want for 2 have it made so its the midpoint between saddle right forward on an inline and right back on a set back, likewise seat tube angle.

This is true(ish), so long as you're going in a straight line. These are the main parameters that affect your position on the bike, but other factors determine how your bike will handle.
If you want to go round corners too, the head tube angle and fork rake will impact the handling. I suspect the chainstay length might also have an impact, but not so sure about that.

Rob, if you want to try a bike with a more relaxed head tube angle, you're very welcome to have a go on my cross bike; drop me a PM. I can bring it to the HC tomorrow if you're going to be there. I doubt it's what you want, but it'll give you a very clear illustration of how head tube angle affects the handling.

Wrath Rob

Il Principe wrote:

If you must have disc brakes, prob best to go Hydraulic.

http://velonews.competitor.com/2012/08/bikes-and-tech/technical-faq/technical-faq-throwing-ice-water-on-road-disc-brakes_235280

Interesting read and some interesting points. As with anything, it depends what you want them for. I want more controllable and consistent braking in wet conditions, particularly when commuting. That feeling of grabbing the brakes and nothing happening while the pads clear the water/crud off of the rims is pretty scary. Outright power isn't a concern as I know I can send myself over the handlebars with rim brakes, at least in the dry. I'll also not be heading up/down too many long climbs on it so the weight/heat management problems raised in the article, while valid, are less of a concern.

Ideally, I'd wait for hydraulic brakes and STI shifters, but this looks like being a little way off and will probably be expensive to start with. I'm after a bike before the end of this year, and I can always upgrade to hydraulics once the price becomes more reasonable in a year or 3's time!

mtb-idle

I cracked my ti frame altho it was an MTB .

Based on the money you are likely to be spending you really, really don't want to be guessing these things (or taking advice from 'some bloke on the interweb').

I know Mike at dialled bikes well (in fact the ti frame i cracked was one of his prototypes). he first got into the business by wanting to build his own ti frame. This involved many, many hours of drawing using CAD software plus prototypes (plural) being built, shipped to him, built up, ridden, tested, adjustments via CAD made, revised drawing signed off, next prototype being made and shipped etc.

And this was for someone who already knew a hundred times as much about frame geometry as I will ever know.

Now i know there are many people out there offering custom builds but I really think that unless you are extremely knowledgeable about frame design you need to be lead by them rather than spec'ing up some frankenbike that looked good on paper but rides like a dog.

Just my opinion of course and good luck, I'm sure you will enjoy the process.

il_principe

Wrath Rob wrote:

Il Principe wrote:

If you must have disc brakes, prob best to go Hydraulic.

http://velonews.competitor.com/2012/08/bikes-and-tech/technical-faq/technical-faq-throwing-ice-water-on-road-disc-brakes_235280

Interesting read and some interesting points. As with anything, it depends what you want them for. I want more controllable and consistent braking in wet conditions, particularly when commuting. That feeling of grabbing the brakes and nothing happening while the pads clear the water/crud off of the rims is pretty scary. Outright power isn't a concern as I know I can send myself over the handlebars with rim brakes, at least in the dry. I'll also not be heading up/down too many long climbs on it so the weight/heat management problems raised in the article, while valid, are less of a concern.

Ideally, I'd wait for hydraulic brakes and STI shifters, but this looks like being a little way off and will probably be expensive to start with. I'm after a bike before the end of this year, and I can always upgrade to hydraulics once the price becomes more reasonable in a year or 3's time!

Fair enough. I still think they are overkill for a London commute though. The stress they put on the fork would concern me as well.

rolf_f

UndercoverElephant wrote:

There wasn't any perceivable rust anywhere in that area of the frame either. If it had been a better frame, it would have been off to Bob Jackson's for a downtube transplant, that would be much harder to do on Ti.

This is the point - any frame can break, no matter what. A forever frame really ought to be repairable. Steel with lugs is surely the easiest solution in this respect.

Anonymous

Rob - Just wondering why you want a bike for life?
Someone else on here was looking at something similar and eventally went Fu*k it (for the reasons below) and got an S-Works!
You're only gonna get older, less bendy and slower and probably need a change anyway in the future so treat yourself then. Why not buy a sportscar equivalent? Would be much more fun.....

tgotb

Rolf F wrote:

This is the point - any frame can break, no matter what. A forever frame really ought to be repairable. Steel with lugs is surely the easiest solution in this respect.

Carbon is much easier to repair than steel (though it's not an ideal material for a bespoke frame, so not that relevant to the OP...)

Wrath Rob

Thanks all for the advice, its always interesting to have your thoughts challenged. If you can't examine and respond to them then you're not going to be on the right path.

@TGOTB: Thanks for the offer. HC?

@Il Precipe: Fork is likely to be the new Enve Road Disc fork. Based on their Cross disc fork, so I'm happy that its up to the job.

@MTB-Idle: The frame is from Qoroz, so definitely not some dodgy Alibaba outfit. Its through Velosport in Putney so all nice and reputable. I've been in contact with Chris from Qoroz who's done the design and talked me through the reasoning for it, so I'm happy that I'm in good hands. I'm just struggling to convert comments about head tube angles giving increased stability into how that will feel in relation to my current bikes.

@Coriordan: This is going to be a sports car! Well, more of a GT than an out and out sports car. I'm fortunate that I can run more than 1 bike so I've already got a fast Sunday bike, which I'm sure I'll replace at some point in the future, maybe even with an S-Works. This bike will be more comfort orientated for the reasons already raised. Having said that, if its a complete slouch then I won't be too happy!

supersonic

Maybe test ride a few other bikes if you can, noting the geo?

I have to agree with the others: ti is not always for life, nor is it always supple. Unless the frame builder build suppleness into it, but he can do it with any material.

I'd wait a while, do a bit more research, a bit more riding!

tgotb

Wrath Rob wrote:

@TGOTB: Thanks for the offer. HC?

KW Hill Climb tomorrow. I'm driving down there (to save legs for race on Sunday) so easy to stick an extra bike on the car if you're going to be there. If you're not going, I'm sure we can arrange something else...

walkingbootweather

Rob, I went through a similar thought process about 4 years ago. I designed a Ti frame to be made up in China and specced mainly Ultegra level kit for a total build price of about £1300, although to be fair I cashed in a few favours to get some of the kit at cost price.

How did I design the geometry? Well it was based upon bikes I already had or was familar with, but I also poured over details of other bikes that I liked or lusted after. Apart from the odd sportive or day trip when I've been caught out by the weather the bike has been very well looked after and (touch wood) I've not had any issues with build.

A friend of mine was minded to go through the same process to I did put together a document with all details of design, component cost, pictures etc. If this of any interest pm me your email address and I'll send you a copy.

Good luck.