Changing fork rake to address toe overlap?

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wheelsONfire
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by wheelsONfire

iamraymond wrote:
Fri Mar 17, 2023 9:16 am
I know I know I know.... toe overlap is a problem with the rider not the bicycle and I should just get used to it.

One of my bikes (2016 Litespeed T7) has terrible toe overlap compared to my other bikes. It is a size small (50cm) and has a 72.5 HTA paired with an Enve 2.0 fork with 43mm rake. I've already switched from 170mm to 165mm cranks and use my narrowest shoes when riding this bike. But I'm still experiencing overlap. I already had a close call while climbing really steep switch backs. I typically ride the longer, less steep line around the curve, but if a car is descending then I'm forced onto the steeper inside line which requires turning the front wheel. A small touch of the front tire while going full gas off the saddle can lead to a crash.

So I am thinking to replace this with a fork with 50mm rake. What I've seen from bike builders (like Pegoretti) they fit 50mm rake forks on frames 53cm and smaller and a 45mm rake for larger frames. This should push the front wheel forward a bit, but I don't know if it's enough to make enough of a difference. I know that this change will make the bike more twitchy, but I should be able to get adapted to it.

Any thoughts on this change? Would a 7mm change in offset make enough of a difference?
Yes, i have that on my Open. For sure a sound option!
Bikes:

Ax Lightness Vial EVO Race (2019.01.03)
Open *UP* (2016.04.14)
Paduano Racing Fidia (kind of shelved)


Ex bike; Vial EVO D, Vial EVO Ultra, Scott Foil, Paduano ti bike.

Hexsense
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by Hexsense

IvanZg wrote:
Fri Mar 17, 2023 1:47 pm
Place your shoes on the pedals and simulate situation where you overlap with the wheel and see if 7mm will be enough
Adding 7mm of fork rake to the fork adds more than 7mm to your toe clearance when you turn the bar due to how the wheel not only rotate but also translate away from you.

72.5 degree HTA + 50mm fork offset will result in low trail value. Not much else can correct that. However, using bigger tire (like 28mm tires instead of 25mm) will help increasing trail value a bit. But that bite back in reduced toe clearance again...

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iamraymond
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by iamraymond

jih wrote:
Fri Mar 17, 2023 2:02 pm
You should have to be turning quite sharply before you get toe overlap then - basically a u-turn. Are the vehicles coming the other way taking up most of your lane too, so you're left making an extremely tight bend?
Yes that's exactly it. I'm stuck going up the inside line because a car is come downhill on the less steep wider line.
jfranci3 wrote:
Fri Mar 17, 2023 2:58 pm
If you're 2x in front, I'd do the angle headset before the BB. At $300, I'd still do the headset first. The fork offset will give you less trail (stability), the headset will give you more stablity. I wouldn't worry about the handling too much as you're not changing the chainstay length, so you won't change your percieved handling. You are changing the wheelbase in any case, so that will impact your extreme low speed handling (basically, your turn radius).
Did you measure the overlap?
Do you know the direction of the offset with the fork mounted? I doubt you get all 7mm, it proabably nets out to 6mm with the rake depending how they measure it, so I wouldn't cut it close.

What wheels are you running? If you go wider internal, it'll oval out a tire a bit, so that'd give you 1-2mm. Maybe borrow a wide rim from someone to try that.
I found this product (link) which could slacken the HTA from 72.5 to 71.5. Seems like that could be a good option instead of replacing the fork. I have a 1 1/8 steerer and a 34mm non-tapered head tube so it should work.

I just measured and the front 3cm of my shoes overlap the tire. The front wheel is only turned slightly (maybe 10 degrees?) in this picture and you can see how much of my shoe contacts the tire.
IMG_7032.jpg
Changing the fork offset from 43 to 50mm will move the wheel forward. That's what the geocalc tool also showed, but I cannot tell by how much.

I'm using 28mm GP5000s on a DT Swiss PR1400 Oxic wheelset (18mm internal). I've ordered 25mm GP5000s to see how much that can help. The 28mm tires only measure to 27mm so they're probably bulging out a bit. Hoping the 25mm tires will gain some clearance. Trying a wider wheel is a good idea as well.

apr46
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by apr46

I would rather swap the fork than mess with the head angle. As long as you match the axle to crown of the current fork with the new one, it should be managable. Trail is less about the absolute handling of the bike and more the feedback you get back from the bike. Changing the head angle will change the actual handling limits of the bike.

The resulting trail of the fork swap should be in the 54-55 mm range. While this is on the sharper end of a modern bike, the new Ritte Espirit will be similar and the Lapierre Xelius is even sharper for its M-XL bikes. The smaller trail may even be preferable with narrower bar if you end up going that way.

You will also be lengthening the wheelbase, but nothing crazy either.

I ride a bike with a 51-52mm trail and narrow bars and happen to really like it.

Whether or not this is worth it to resolve toe overlap is a different matter.

Edit: also shorter cranks would help...if those arent in the consideration set

ABogle
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by ABogle

I have about as much toe overlap as you do on any bike that fits me so I can see where you are coming from but you need to understand that there is a reason no off the shelf bikes are rarely designed to have 52mm or so trail, especially as you will not have a wider tire to offset some of that low trail.

I had a bike that came with the wrong fork (it was the 50mm version mean't for the larger sizes), this gave the bike a trail figure of 51. Personally, I really hated the way it handled, I had no confidence in it, I just couldn't pick and a hold a line around a corner. This can be offset a bit by having a long stem and to be fair my cockpit was quite short (100mm stem & 75mm reach bar). Anyway point is, there will be compromises to the approach you are seeking.

apr46
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by apr46

When a bike is designed, I like to think that an engineer spends quite a bit of time making sure the geometry is balanced. Either option, changing the head angle or moving to a higher offset fork both will mess with that. I personally would rather tolerate toe overlap (or redo my fit with shorter cranks) than experiment with that on a production bike. In terms of which one would change the character of the bike more, I find that slackening a bike has more effect than reducing trail.

They also change the bike in different ways. Slackening the head angle will make the bike more stable. Reducing the offset will more likely mute feedback from the road, and as you mentioned will change the way the bike feels which may make finding the limits of handling or the right line more difficult. In this situation, with this geometry, if I had to chose, I would rather change the offset rather than slacken the bike.
ABogle wrote:
Sun Mar 19, 2023 3:48 pm
I have about as much toe overlap as you do on any bike that fits me so I can see where you are coming from but you need to understand that there is a reason no off the shelf bikes are rarely designed to have 52mm or so trail, especially as you will not have a wider tire to offset some of that low trail.
Trail is not a magic parameter to design a bike around and there is variation in the trail of top level race bikes. Within the more common sizes the trail on the Tarmac Sl7 varies from 63-55mm (size 54 is 58mm), Supersix Evo 4 is at 58mm, the Emonda from 68-56mm (size 54 is 56mm), and the Xelius SL between 58-52mm (size 54 is 52mm).
ABogle wrote:
Sun Mar 19, 2023 3:48 pm
I had a bike that came with the wrong fork (it was the 50mm version mean't for the larger sizes), this gave the bike a trail figure of 51. Personally, I really hated the way it handled, I had no confidence in it, I just couldn't pick and a hold a line around a corner. This can be offset a bit by having a long stem and to be fair my cockpit was quite short (100mm stem & 75mm reach bar). Anyway point is, there will be compromises to the approach you are seeking.
While it would require finer steering inputs, you actually should have gone the the other way to balance the leverage of your inputs with the steering geomtry and moved your hands closer to the steering axis. A narrower bar, for example would have helped.

Hexsense
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by Hexsense

apr46 wrote:
Sun Mar 19, 2023 5:30 pm
When a bike is designed, I like to think that an engineer spends quite a bit of time making sure the geometry is balanced.
On a medium (54) size bike.
Good manufacturers adjust head tube angle and fork offset together so that all size handle similarly ( not neccessary the exact same trail value, just reasonably close enough).
Careless, financial-lead designers just slacken HTA without compensating it with more forkset on smaller bike.

See the whole geometry chart of every size. Do you see multiple head tube angle across size range?
If so, do they also use multiple fork offset appropriate with the HTA? Then you can tell if they care for size smaller than medium or not.

You already listed some good example brands. Here, these are some bad ones: Canyon and Giant

apr46
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by apr46

^Ok fair point. Brands may be cheaping out by not wanting to have more than 1 fork offset. Most seem to have at least 2 though. Then there is Cervelo with 3 on the R5, even though the 54-61 use the same front end geometry.

If you go throught the exercise of maintaining the same weight balance, assuming riders in the middle of each size range, try and keep the wheelbases reasonable, but are open to using 3-4 fork offsets; one of the interesting things is that you end up with similar trail numbers even if they arent the drivers of the geometry.

Larger and smaller bikes are also full of contradictions driven by fit. Ideally a steeper head angle should be paired with a lower BB, but you rarely see that because that creates pedal clearance issues. Smaller bikes end up slacker because of reach limitations and wanting to maintain weight balance without voilating min. chainstay lengths for groupsets.

iamraymond
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by iamraymond

Great discussion and points made so far. Thanks for your insights.

I checked the geometry chart for my frame and saw that all sizes use the same 43mm fork although the HTA varies from 72.5 for size small to 73.0 for a large. The geometry of their current frames also use the same fork rake across sizes so I question how much they considered matching the handling characteristics to between sizes. I could see that for brands like Cannondale, Cervelo, Specialized, but not so much for smaller builders like Litespeed especially if they're dealing with frame only customers.

I would keep the axle to crown lengths the same at 367mm if I were to change the fork. I contacted Works Components and their eccentric headset should be back in stock in a few weeks. The eccentric headset would push the front wheel 2mm further forward compared to changing to a 50mm fork. I'd gain a bit more clearance with the headset. Honestly, I usually take it easy while descending so I'm not pushing the limits of my bike's handling. My priority is more of the toe overlap.

I'm already on 165mm SRAM RED cranks and they don't offer anything smaller than that. I'm hoping 25mm tires will help.

satanas
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by satanas

Unless you really like the bike apart from the TCO a better solution might be a different frame, with more reach and/or a slacker head angle and more offset.

As for handling (and trail), preferences and opinions vary widely as to how things should be. If the range of HTAs for the different frame sizes is really only half a degree across the range, then IMHO there's no reason to vary the fork rake - except that doing so (+ the HTA) would at least partially solve the TCO issue.

FWIW, I also dislike TCO, but in practice a small amount is usually bearable - 3cm is however not a small amount. At least you don't have mudguards (aka fenders)!

iamraymond
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by iamraymond

I fitted 25mm GP5000s and I’ve gained a bit of clearance compared to the 28mm. The tire height is 3mm less. We’ll see if this extra clearance makes a discernable difference on the road.

I do like the bike, but the overlap is just part of riding a size 50 or 51 frame with cleats positioned all the way back. I’ve only owned one bike that didn’t suffer from any overlap so switching frames doesn’t guarantee it won’t happen again.

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by Gazelleer

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kgibbo1868
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by kgibbo1868

Could you adjust your cleat position to move your foot back a bit?


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iamraymond
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by iamraymond

I could move the cleats, but this is how my shoes were setup after a bit fit so I don't really want to mess with it.

satanas
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by satanas

Hopefully when one's position is sorted, one's bike will comply with it easily. Or one could adopt the Borg approach to bike fit, "Resistance is futile - you must comply!"

If things aren't so great one must deal - or swap frames. I wouldn't change position and compromise fit unless something was really off.

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