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Derailleur size for a newbie

Posted: Fri Aug 30, 2019 17:05 pm
by jayptrp
Hi everyone!
My 6 year old son has a 20 inch MTB with a single chainring upfront, and 6 speeds in the rear. I'm thinking about upgrading his freewheel to a 6/7 speed with a 34t.... Only because its quite hilly where we live and having a lower ratio will certainly help my son on the steep uphills. I know I have to change the derailleur to a larger cage as the current one only has a sprocket limit of 28t. My concern is will a larger cage derailleur be too big for a 20 inch wheel bike that there'll be a risk of the bottom pulley hitting the ground/tyre?
Many thanks
Jay

Re: Derailleur size for a newbie

Posted: Sat Aug 31, 2019 08:42 am
by steve_sordy
Leave the freewheel as it is and fit a smaller front ring.

Re: Derailleur size for a newbie

Posted: Sat Aug 31, 2019 14:24 pm
by jayptrp
Thanks, that was my alternative plan. Although downsizing the front ring will compromise (a little bit) his speed on level ground. Seems like a good compromise, thank you.

Re: Derailleur size for a newbie

Posted: Sat Aug 31, 2019 14:40 pm
by steve_sordy
jayptrp wrote:Thanks, that was my alternative plan. Although downsizing the front ring will compromise (a little bit) his speed on level ground. Seems like a good compromise, thank you.


Unless you increase the range, by changing the cassette as you were considering, then that is what would happen. But you only said he wanted to go up steeper hills.

Re: Derailleur size for a newbie

Posted: Sat Aug 31, 2019 15:48 pm
by jayptrp
My son spends most of his time on 2nd and 1st so I think you're correct, changing the front ring would make more sense as this will give him more access to the other gears. It will be cheaper too I guess.

Re: Derailleur size for a newbie

Posted: Sat Aug 31, 2019 18:20 pm
by steve_sordy
jayptrp wrote:My son spends most of his time on 2nd and 1st so I think you're correct, changing the front ring would make more sense as this will give him more access to the other gears. It will be cheaper too I guess.


Another change that you could make that may make sense to your son is to change from gripshift to trigger shift. Yes I know the smaller bikes tend to have gripshift, but as soon as I changed to trigger shift my grandson absolutely loved it. Engaging the larger rings required too much twisting force from him. But trigger shift was the same easy to apply thumb pressure for every gear (going to bigger gears).

Another tip: Work out the weight of his bike as a % of his weight and compare it to you and your bike. :shock:

Re: Derailleur size for a newbie

Posted: Sun Sep 01, 2019 07:44 am
by jayptrp
Thanks. I have already changed the gripshift to a thumb shifter and my son loves it. I'm just having difficulty looking for a smaller front ring that would fit his bike.

As for the weight, hi bike is 66% of his weight whereas mine is 19% of my weight :(

Re: Derailleur size for a newbie

Posted: Sun Sep 01, 2019 18:12 pm
by steve_sordy
jayptrp wrote:T...........

As for the weight, hi bike is 66% of his weight whereas mine is 19% of my weight :(

Now you know why he struggles to keep up with you!

Look at bikes from Islabike, Hoy and Frog for lightweight kids bikes. Yes they are more expensive, but the second hand value is amazing! Check eBay for those brands and see what they are going for. When I used to buy Islabikes for my two grandkids, the average cost of ownership was much less than 79p/week for each bike. I'm now selling a Hoy Bonaly 24 on eBay and I expect to get a great price for it. But the buyer will save well over £100 vs current new and get a well looked after bike that looks like new.

Re: Derailleur size for a newbie

Posted: Mon Sep 02, 2019 13:02 pm
by larkim
Agree on the expensive / light / good resale equation. I've had a Frog bought for £270, sold for £150 I think after nearly 3 years of good use. Now onto a Hoy Bonaly which would have a similar cycle. If I'd be told I could get a Frog for £120 brand new I'd have bitten your hand off!!

Re: Derailleur size for a newbie

Posted: Mon Sep 02, 2019 18:48 pm
by jayptrp
Makes sense buying lightweight second hand bikes in those brands. But let's not forget I'm a newbie at this, only started to read more and more about bikes 2 months ago after buying my son's first mtb. He went for what seemed cool and I went along with it as he was happy. He wanted the apollo xpander! Which at the time seemed OK as the bike looked the part and me being a complete idiot bought the bloody bike for him. Everything has since been an afterthought. After a few cycling trips we started changing things like shifter, tyres, handlebar, brake levers.... The aim is to make the bike a little bit easier for him. That's why I'm thinking about changing the front ring to a smaller one. We're kinda committed to this bike and my son is still besotted with it. I did show him isla, frog and hoy bikes but the answer was a firm no as he wanted his bike with dual suspension, Problem is it's so difficult to find a 32t/34t front ring with a short crank (140mm).

Re: Derailleur size for a newbie

Posted: Mon Sep 02, 2019 18:53 pm
by jayptrp
Being beginners we'll build up gradually. It also doesn't help that I havent got a circle of friends who are into cycling so this is an entirely new world for me :) We're only cycling for leisure at the moment but I can see this becoming a regular hobby especially we live close to Betteshanger Park.

Re: Derailleur size for a newbie

Posted: Thu Sep 05, 2019 12:11 pm
by jayptrp
Hi all. Right, following your advice I'm now looking for a lightweight bike and my choices are
Voodoo sobo
Specialized hotrock
Carrera blast

These are not as light as frog/hoy/isla but they're still a lot lighter than his current bike and not as expensive. I've convinced my son to not have a bike with rear suspension but the front suspension is whre we'll compromise. What do you suggest? Thanks

Re: Derailleur size for a newbie

Posted: Thu Sep 05, 2019 14:35 pm
by edward.s
On the crank front, Frog sell their childrens crank sets separately on their website so that is an option for the old bike.

Depends on budget. the issue with small adult bikes for kids is that the cheaper spring forks won't work very well with lighter weight children as you can't alter the spring much if at all. If you move to an air shock adult bike you are talking much more money, but at least you can run low pressure in the shock so the kid gets full travel.

My son was in the same place and we ended up getting him a Frog 72 which is 26" wheels, air shock and 1x9 gears. We also looked at a Whyte with similar spec but a good experience with a previous Frog 62 made us go for the Frog 72 in the end. Neither of those are particularly cheap options at around £600 new, but maybe secondhand they might work for you and they'd be a good ride for a child. Certainly my son, who is 8, can do everything on his I can do on my 29er 130mm hardtail.

Re: Derailleur size for a newbie

Posted: Fri Sep 06, 2019 12:02 pm
by philcubed
My daughter had a Specialized Hotrock 20" (bought second hand for £50, sold for £100!). it was a heavy bike for her, and the fork didnt move at all.
She has just grown out of her Carrera Luna 24" (girls version of the Blast), she found this easier to ride, expecially after changing out the twist grip for trigger shift, but the fork still didnt move much (it is a Junior fork). I bought this second hand for £100 and am expecting to sell it for much the same.
So these bikes can keep their value at re-sell, but the Hotrock I would say is too heavy for a small child.

Re: Derailleur size for a newbie

Posted: Fri Sep 06, 2019 14:54 pm
by steve_sordy
I have just sold my grandkids' Hoy Bonaly 24. It is a 24" wheeled rigid with 8 gears, a good range at the back and trigger shift. I paid £320 for it 4 years ago and I sold it for £215. They are now £360 new. When I bought it, the Bonaly 24 was the same weight (9.2kg, 20.3lbs) as the Islabike Beinn 24, but the Hoy had gears and shifters better suited to mtb.

So it cost me £105 over 4 years. I paid £15 for bike tape to protect the frame, fork and stays. I paid £20 for two mtb tyres and refitted the original tyres for sale. So over 4 years the bike cost me £140. At £2.92 that is less than a pint of beer per month! In addition my grandson, then my granddaughter, had a very good quality and super lightweight bike to ride. :D

Edit: To stay consistent with a previous post of mine, that is 67p/week!

Re: Derailleur size for a newbie

Posted: Sun Sep 08, 2019 09:08 am
by jayptrp
Decision made, bike now bought. Voodoo Sobo 20 it is. As we'll be using trails more than roads I guess the extra 2 kilos over hoy/frog/isla is a reasonable compromise as this bike is still 5 kilos lighter than my son's old one. He's given it a go and so far he's really enjoying it.