Discussion: Bike handling of modern small bikes.

Discuss light weight issues concerning road bikes & parts.
istigatrice
Posts: 822
Joined: Sat May 12, 2012 8:32 am
Location: Australia

by istigatrice

Not sure how relevant this is, but IME trail and front centre matters a lot with smaller bikes. Had two bikes with ~71 degree head angles (71.3 and 71.5) paired with fork rakes (50 and 43 respectively) and the 71.3/50 combination handled significantly better than the 71.5/43 combo. In fact I prefer it to a 73/43 combo, which is to say it's brilliant rather than just very good/excellent. It's interesting to note that the front centre of the 71.3/50 is within a few mm to the 73/43 despite the top tube being ~20mm shorter (seat tube comparable - 73.7 vs 73.5).

So at least from this anecdotal evidence it seems like trail (and possibly front centre) matter a lot. In fact if I throw in my track bike (74.5/30) it's got a similar trail and front centre again and handles really well too - so I'd suggest as long as you have the "correct" fork rake use the head tube angle to obtain the desired front centre (for a given reach). I suppose there are limiting cases but both the 71.3/50 and 74.5/30 worked really well for me, and I think both were selected to 'manage' the front centre distance to within a few mm's despite vastly different reach/top tube lengths.

Or perhaps I've been 'conditioned' to think this is how a bike should handle given 4 of my bikes have such similar trail/FC numbers, and so as soon as I get something different (71.5/43) it feels "off".

EDIT: to add to this, I don't think the chainstay length matter, since my track bike has super long drop outs (so I can use the same length chain for a 90in vs 120in gear) and I don't notice any difference in handling when I have the wheel all the way back, compared to all the way forward. I think there's a good 30-50mm worth of adjustment there)
I write the weightweenies blog, hope you like it :)

Disclosure: I'm sponsored by Velocite, but I do give my honest opinion about them (I'm endorsed to race their bikes, not say nice things about them)

Hexsense
Posts: 591
Joined: Wed Dec 30, 2015 12:41 am

by Hexsense

I have a question about company that make one fork fit all size.
Why do they settle on 43mm fork rake and 73 degree head tube angle as standard?
Why don't they build every size with 48mm fork rake and 72 degree head tube angle instead?

Both gives the same trail number. It would help small size tremendously while also work on bigger bike without any negative effect on trail number and handling.

by Weenie


2lo8
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Joined: Thu Mar 31, 2016 10:32 am

by 2lo8

Same reason they don't make lots of XXS and XXL cranks. The bell curve.
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istigatrice
Posts: 822
Joined: Sat May 12, 2012 8:32 am
Location: Australia

by istigatrice

Hexsense wrote: ↑
Sun Jul 01, 2018 5:58 am
Why don't they build every size with 48mm fork rake and 72 degree head tube angle instead?
The front centre will be waaaaaayyyyyyyy too long on anything larger than a "small" (thinking 53-54 ETT with 73-74 degree set angle), and would still be too short for an XXS or XS, so this kinda 'flops'.
I write the weightweenies blog, hope you like it :)

Disclosure: I'm sponsored by Velocite, but I do give my honest opinion about them (I'm endorsed to race their bikes, not say nice things about them)

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skidrrr
Posts: 16
Joined: Fri Jun 29, 2018 12:25 pm
Location: Moldova

by skidrrr

I kinda fear to corner on huge speeds... Of course it's a techical skill that I'm going to improve... but after reading this thread I was hopping to understand how frame can contribute to it.

Image
For example I know that Nairo Quintana is one of the best descdenres and he has Canyon Ultimate XS and Canyon has the biggest trail. Then again I watched Kenny Elissonde who is riding on Dogma even smaller size than in my table and still he was fast enought while Dogma's train is big. According to this chart SL6 will be the best choise for good handling. It is that simple?

P.S. please ignore weight values, they aren't correct. I just filled in what I remembered aproximately

Marin
Posts: 3132
Joined: Wed Jan 22, 2014 11:48 am
Location: Vienna Austria

by Marin

Geometry numbers don't matter much if you are used to them and are focused.

Hexsense
Posts: 591
Joined: Wed Dec 30, 2015 12:41 am

by Hexsense

Long trail may not be deal breaker. It just wanting to go straight by its own more and you have to exert more force to make it turn at high speed.
Low weight and narrow bar amplify effort you need to make it turn tight. How much is too much is hard to tell, but mildly longer is not too bad if you are used to it.

I recall that Canyon Aeroad rim brake version has a flip flop adapter at fork's end to change fork offset. Not sure if it is also apply to the Ultimate. And not sure which fork offset setting is quoted in your table. Also Quintana did well in descending but i don't think he is outstanding. He lost time to Chris Froome on decending Stage 8 of 2016 TDF. Like definitely not as fast as Nibali and Mohoric.

Of all racing bikes, BMC Teammachine 47 is one of the slowest handling around. It match 70.5 degree head tube angle with 41.6mm fork offset creating 76mm trail (with 25mm tire).
Luckily this year Richie Porte will have the new Timemachine Road which has 71.2 degree head tube angle with 50mm fork offset creating a very respectable 62-63mm trail as a better option. Hopefully he won't struggle on downhill like last year TDF.

istigatrice
Posts: 822
Joined: Sat May 12, 2012 8:32 am
Location: Australia

by istigatrice

Marin wrote: ↑
Fri Jul 06, 2018 7:28 pm
Geometry numbers don't matter much if you are used to them and are focused.
Big disagree, unless they're similar trail etc. You can use very different top tubes to achieve the same reach.

But I could never corner well on bikes with over 70 trail, and I've had that kind of bike for years. I got used to being a 'bad' descender, but the minute I get on a 'proper' bike I'm descending much faster. If the bike needs more effort to turn in then it needs more effort to turn in, IME if you're balanced on your bike it's much easier to hold it in a straight line than to carve a corner out.
I write the weightweenies blog, hope you like it :)

Disclosure: I'm sponsored by Velocite, but I do give my honest opinion about them (I'm endorsed to race their bikes, not say nice things about them)

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skidrrr
Posts: 16
Joined: Fri Jun 29, 2018 12:25 pm
Location: Moldova

by skidrrr

Thank you very much for explaining it. Now I have another question.
What is the best choise for small rider in terms of handling?
a. small frame with bad/long trail and 110mm stem
b. bigger frame with good trail number but shorter stem like 80mm

As I see it weight distribution could neglet geometry factor because front wheel is underloaded and therefore variant A is better for corerning and descending.
What do you think?

istigatrice
Posts: 822
Joined: Sat May 12, 2012 8:32 am
Location: Australia

by istigatrice

A different bike - there's no excuse for not speccing a second fork option for smaller sizes. Small brands like SwiftCarbon do it, so I'd say it's compulsory for bigger brands.

I highly doubt you'd need a bike which is 30mm longer in reach to hit 57-65mm trail (only bike which comes to mind would be a BMC team machine). So if that is the case I'd look to a different bike all together. Other than that, I wouldn't hesitate to recommend a 90-100mm stem if that gives you the correct fit on a long reach bike. It's probably what the CONI manual would have recommended for a given size anyway.
I write the weightweenies blog, hope you like it :)

Disclosure: I'm sponsored by Velocite, but I do give my honest opinion about them (I'm endorsed to race their bikes, not say nice things about them)

LM7805
Posts: 8
Joined: Fri Aug 25, 2017 12:56 pm

by LM7805

Being a short person, I find this discussion pretty interesting. I've been looking at the geometry of xs road bikes lately and the vast majority of brands don't change fork offset across sizes. For example, Giant TCR in size XS has a HTA of 71 and a trail of 70! Specialized also doesn't change fork offset, but in all their bikes they seem to go for a steeper HTA. Their allez sport in size 48, for example, has a HTA of 72.25, so the fork trail is only 59mm, which is still quite "normal". Cannondale, in many older forum discussions, were always praised as having good xs size frame geometry in their CAAD8/CAAD10 models. However, it appears that for their newer road bikes such as the CAAD optimo and CAAD12, they have ditched using different fork offsets for smaller sizes which is a shame. Trek is one of the companies that actually uses a different fork rake for smaller sizes. Cervelo also use different fork rake and are more extreme in that they have the same trail of 57mm across all frame sizes.

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