Building a singlespeed TT bike

warrior4life

I have a standard Giant bowery 84 and i want to build into a TT bike similar to the one below.
I just need to know what gearing to use.. Hoping to average 23-26mph on flat course.
Any suggestions or help with bits to buy is much appreciated as im on a tight budget and i cannot believe how much chainrings, TT bars and aero seat posts sell for.

moonshine

you want it fixed, not singlespeed. there is a difference. SS has a freewheel so you can stop pedalling, fixed does not. There is a benefit from going fixed due to the flywheel effect. There is no benefit doing it singlespeed.

If you mean do it "fixed" rather than SS, you need to choose your gearing for your target speed, cadence and how hilly the course is. (there are tables somewhere that have all the fixed cadence / gearing / time / speeds calculated out.) If it is flat, then fixed can work. if it is hilly, then fixed is less that ideal. not saying it doesn't work, just it will be likely to be slower & harder work.

There are tonnes of articles on web e.g Shelfon Brown & velosolo re. going fixed and recent thread here on TT forum
http://www.timetriallingforum.co.uk/index.php?showtopic=50782

G

warrior4life

I can flip the rear hub depending on what i want.
I'll be doing 2 flat 25mile tt's. (a 2 up and a 3 up).. Maybe i'll do more
Ill be doing a cadence of 85-95.
The bike is as much for training as anything, where i live i have miles of complete flat that i like to batter.
I just enjoy doing 30-40 miles fast by myself and i've been riding the bike with normal singlespeed 17-46 spinning out at 27mph, starts to get silly when i get over 22, I wanted to up the gearing and make it a more aero postion.
I've been asked to make up the teams on the TT's and ive always wanted a tt bike (they look so good), i enjoy singlespeed so thought i'd kill 3 birds with one stone (which takes much skill)

I've got my race bike and ive just bought a new winter bike,my cycling pot has £200 max left in it for conversion.

I never thought about the flywheel effect, when i do the actuall TT's I may use it especially if it'll make me faster.

I'll check out sheldon brown... Thanks for the help

moonshine

i don't know anyone who would do a TT on a SS. People do (and do very well ) TTs on a fixed. But most hubs are flip flop, so you can run fixed on one side, SS on the other side for pottering as you say.

I'm not sure i'd ride a fixed in a 2 or 3 up.... they are different from a normal TT in so much you are riding with others and check with your mates that they are happy for you to be fixed if they are geared... the riding styles could be different and this could be difficult to combine

Monty Dog

I generally ride fixed for TTs - SS would be pointless unless you have a long steep downhill and then you still have the extra weight and faff of a rear brake. I would say you have a way to go in terms of developing your pedal stroke if you're 'spinning out' at 27mph on 46x17 - suggest you need to be able to hold a comfortable cadence of 90-100rpm at around 40kph. For TT's I'll run 48x16 or 50x17 - there's a longish downhill on my local course so being able to maintain a high speed is important but not having a painful grind-up on the way back. I'd work on your position and pedal stroke over winter, perhaps increasing your chainring or dropping a tooth on your sprocket as you get smoother and stronger - . Having a smoother pedal action and faster cadence means you'll be able to cope with riding with team mates with gears in a 2 or 3 up - the pace is meant to be constant on the front, the recovering rider is merely easing off as part of the recovery. FWIW my PB on fixed is only marginally slower that my best time on gears. PS you'll find you 'pull' yourself onto the nose of the saddle on fixed with tribars, so decent shorts are a must

warrior4life

By spin out at 27mph i mean thats about as fast as i can go for a few miles but it doesnt feel efficient at all.
At 33 mph i can keep the cadence for a few seconds but dont actually feel like im putting any power down... More just keeping up.

I've been a spinning class instructor for years now and this has given me a great sprint and made me comfortable at spinning a fast cadence, i can spin a faster cadence then anyone i know, the spinning does nothing though for general road riding and racing.

I was thinking if i continued to ride singlespeed when the speed picks up i could do 5-10 fast pedal strokes and then freewheel while drafting, ive found that with bike being pretty light and aero as it is this has been easiest in the past.
I never considered riding fixed.
As im here looking for advice i will use it, I'll flip the rear and go for a 50 x 17 and see how i get on... Ive rode the track a few times but i know it'll take some work to become comfortable with the fixed and position together.
I'll also have to see how i get on riding TT fixed with others, I'll also make sure to have some good shorts. thanks

inseine

That bike looks great BTW!

You really need to work out what speed you can do and what cadence you can manage and that'll give you the gear. Some of your figures sound a bit out of whack. If you're only averaging 90ish on 46-17 I don't think you'll be travelling much quicker than 20.
I did a couple of medium gear (72'', same as your 46x17) 25s and my fastest was 1.04 which is around 110rpm average bit your spinning your a**e off at times. When I upped it to 46x14 I could go under the hour and just under 100rpm. I was on a standard track bike.

warrior4life

Im looking for a gear that with a cadence of 85-90 will be around 23-24 mph.

My cadence is way higher than that, if i do a cadence of 85 i prob do around 19mph at the moment.

inseine

Im looking for a gear that with a cadence of 85-90 will be around 23-24 mph.

Well that's simple! With your 46 ring a 14 sprocket gives you 93rpm @ 24mph, while a 13 gives you 86 @ 24mph.

warrior4life

inseine wrote:

Im looking for a gear that with a cadence of 85-90 will be around 23-24 mph.

Well that's simple! With your 46 ring a 14 sprocket gives you 93rpm @ 24mph, while a 13 gives you 86 @ 24mph.

Easy as that!
Ive just been out on my girlfriends bike (compact) and had it in 17 at the back, Realised a 50x17 would be to spinny.
I've just been looking and its £40 for a 52 chainring that would fit on the sugino messenger chainset, and i'd need a new chain as well.

A 14t sprocket is by far the cheapest and easist way forward... Thanks again for the stellar advice

I want to build it as cheap as possible and if i like it splash on a TT bike, If i love it i'll probably just splash out on a new chainset and nice full aero bars.

I tried Sheldon brown and it was a cool site but i found the full gear ratio thing a little confusing.

inseine

You should be able to pick up a Mike Burrows Giant aero seat post up for less than £30 on ebay.