[R332]

I am trying to wrap my head around how various factors influence weight on the front tire and how that impacts front end cornering grip and steep climbing stability.

My first question has to do with stem length because as a tall rider my handlebars are much further away (vertically) from the tire's contact patch than for a shorter rider but this also means my weight is further aft for a given stem length. Let's compare the same bike in two different sizes, both with a 67.5deg HTA.

Bike 1 Baseline smaller bike - 10cm headtube, 60mm / 6deg stem, no spacers under stem

Bike 2 Taller rider bigger bike - 13cm headtube, 60mm / 6 deg stem, 30mm of spacers under stem

Bike 2 has 23mm less effective total reach than Bike 1 meaning, I think, that there is a lot less weight on the front tire of Bike 2 for cornering grip and steep climbing stability. Put another way, Bike 2 would need an 86mm / 6 deg stem to equal the same final forward weight point of Bike 1. Surely this is significant when talking about handling, traction and body position on the bike, especially on the new Long, Lower, Slacker trail bikes that require the rider to be more 'over the front' to get the most of out the new-style geometry? My thinking is that for taller riders / bikes it would be beneficial to keep the frame Reach number more conservative and add cockpit space with a longer (20-30mm) stem vs a standard small/medium bike set-up for a shorter rider with an optimal 50mm stem, to keep the front weight more or less the same for the bigger bike.

My second front end weight question is - what happens when the chainstay length changes? Lets assume a large bike with 500mm of reach, 829mm front center and 432mm chainstays. What happens to the weight distribution when the chainstays grow to 442mm (+10mm) but everything else stays the same up front? Does the front tire gain or lose weight, aka traction?

 

[ccm]

^ Sacrilege burn him at the stake, for disagreeing with the bro dude fashion police

Actually I agree with you and find that short stems makes the steering feel squirrely, except when pointed down hill

 

[Fleas]

Right now I have a 80-90mm stem on my XL AM HT. It takes some fiddling to match everything to one's riding style.

The only counterpoint I might suggest is that with a steeper seat tube angle, the front gets more weight.
Longer CSs also increase weight to the front, but at the cost of extending the wheelbase, which I dislike.

-F

 

[OLDFATUGLY]

Here is my experience dealing with LLS. This Aug. I was the recipient of a new warranty frame (‘21) So, it is LLS when compared the 2016 it replaced. When I had first completed the build, it was out of balance. After fiddling with touch points and adjustments the changes boiled down to; moved the seat forward (significantly), moved the adjustable chain stay sliders back (+10mm). Then for a comfortable ride position I added 20mm in bar width, and -10 mm for stem, this help offset the long TT. Finally after 3 months of fiddling the ‘21 has the balance the ‘16 had.

 

[idividebyzero]

Here is a tall rider giving instructions on how to turn

His stem looks about as short as possible, probably 32mm. If the bike is from a reputable brand then the geometry is fine, if you stray too far from how the bike was designed then almost always the handling gets worse. You just have to ride with a body position and technique that matches the style of bike you have, trying to make the wrong bike match your style is a losing battle.

Long stems dont work unless the head angle is really steep like a road bike.

Steep HA = more steering input when turning the bars
Slack HA = more steering input when leaning the bike

A long stem on a slack bike is a recipe for disaster because as you rotate the handlebars your weight goes in the opposite direction you want, then the longer the stem the more it acts as a lever creating an inconsistent force as you lean the bike over.

 

[PhillipJ]

In my experience seat tube angle is the biggest factor for keeping the front weighted when climbing, assuming the bike actually fits the rider. Longer rear centre also helps but not as much.

Comparing my two trail bikes, one is 440mm chainstays, ~76 STA, 510mm reach with a 40mm stem and the other 430mm chainstays, ~74 STA, 480mm reach with a 50mm stem. I can be more passive climbing on the longer bike, the front stays planted without any thought or effort.

They have similar total stack, the bigger bike has 30mm more frame stack but the smaller bike has 30mm riser bars on it.

 

[Stewiewin]

I am trying to wrap my head around how various factors influence weight on the front tire and how that impacts front end cornering grip and steep climbing stability.

My first question has to do with stem length because as a tall rider my handlebars are much further away (vertically) from the tire's contact patch than for a shorter rider but this also means my weight is further aft for a given stem length. Let's compare the same bike in two different sizes, both with a 67.5deg HTA.

Bike 1 Baseline smaller bike - 10cm headtube, 60mm / 6deg stem, no spacers under stem

Bike 2 Taller rider bigger bike - 13cm headtube, 60mm / 6 deg stem, 30mm of spacers under stem

Bike 2 has 23mm less effective total reach than Bike 1 meaning, I think, that there is a lot less weight on the front tire of Bike 2 for cornering grip and steep climbing stability. Put another way, Bike 2 would need an 86mm / 6 deg stem to equal the same final forward weight point of Bike 1. Surely this is significant when talking about handling, traction and body position on the bike, especially on the new Long, Lower, Slacker trail bikes that require the rider to be more 'over the front' to get the most of out the new-style geometry? My thinking is that for taller riders / bikes it would be beneficial to keep the frame Reach number more conservative and add cockpit space with a longer (20-30mm) stem vs a standard small/medium bike set-up for a shorter rider with an optimal 50mm stem, to keep the front weight more or less the same for the bigger bike.

My second front end weight question is - what happens when the chainstay length changes? Lets assume a large bike with 500mm of reach, 829mm front center and 432mm chainstays. What happens to the weight distribution when the chainstays grow to 442mm (+10mm) but everything else stays the same up front? Does the front tire gain or lose weight, aka traction?

stem length is main, XC bikes w long stem put weight in front.

 

[PhillipJ]

Riding a short frame with a long stem does load the front wheel but we tried that for quite a few years and it turns out that it sucks unless you're climbing.

Some serious business XC bikes are still going the long stem thing but it's gone for a reason for trail and AM bikes.