Ive a new bike ordered (road) and tho i know what reach feels good (saddle tip to bar) . But that is with a 90mm saddle to bar drop. It occured to me that the same measurement but with only a 30mm saddle to bar drop will actually feel shorter and requires a longer distance for the same feel.

Does this make sense? Ive no bike at the min but tested with a mates bike and some string. And when i dropped the saddle 60mm the stem was about 20mm too short

Any online things for working this out as i can spec length of stem prior to delivery

Hope that makes sense
Thanks

RattleCAD?

There isn’t a calculator that’ll work this out for you unfortunately. Your best bet is to buy three stems 10mm apart in length and then go from there.

Dropping your saddle 60mm won’t help matters.

Your saddle height is a constant; it needs to be set to what it should be. Your saddle to bar measurement is the other constant (although you can vary it slightly between bikes). Another useful number is saddle to bar drop.

You should be able to work it out from there. Bear in mind that if you lower the bars then you may need to come forward with the saddle, and likewise if you raise the bars then it may need to go back slightly.

That looks very good but still not sure it does what im after i suspect a maths programme may be what i need. I’ll give tape and string another whirl thanks

Its the saddle to bar height that is gonna be changing david. Last bike saddle to center of bar was 504mm and saddle to bar drop was 90mm . But new bike with saddle at correct position puts saddle to bar drop at about 30mm.

So saddle height is a constant but the bars are raising 60mm. And im happy with that too but im worried that due to the much shallower drop it will feel much smaller

I get you. Was your 90mm saddle to bar drop your ideal? If so, how come you’ve bought a bike with higher bars?

Well reach wise it was but it was a race bike but this is a tourer im getting with a higher front and which will be better for that. But like i say i was concerned if i got the same saddle to bar but with less drop it would feel short

Ive just been playing around with string it seems by using the floor and an imaginary headtube it has less effect than moving the actual seat on my mates bike. I think it seems about 10mm longer would be needed

I may have to ask builder if i can either lend a couple of stems or drive up its a 7hr round trip but its an expensive bike so probably worth the trip to make sure it feels right from the off

Ah right. On a tourer I’d guess you’d be sat more upright, so a shorter reach to the bars will probably be required anyway. I’d also suggest a wider saddle for a more up right position (I guess that’s why Brooks saddles are popular on tourers).

2 things going on:
Raising the bars moves them toward you due to head angle. That can be calculated using trig, or an online triangle calculator. From memory, a 20mm change on a 73 degree head angle is about 6mm or somewhere near there.
Then the second triangle calc is from bar to saddle using the lower drop but also the shorter effective TT due to above.

Try this stem height & reach calculator , it gives you a visual perspective on changes

Also, there’s no point in driving to whereever. Just buy a load of stems off ebay or from somewhere cheap; you should be able to find them for less than a tenner a go.

If you bring the bars up then you may need a longer stem for reach. Raising the bars opens up the hip angle.

Assuming you have a 72 degree head tube (tourer) then for every cm drop there will be an increase in reach of Tan(18) = 0.32 cm. A drop of 3cm will give you a cm increase in reach.

I’d consider a stem 1cm longer to have a similar feel to your race bike.

Makes sense . But another spanner in the works is a shorter reach flared drop so to make sure its right im gonna drive up. As i can try all the options and drive my baby home.

David at over 4k i want a matching stem and seat post 😉 as ive got to live with the bike forever or my mrs will castrate me its gotta be bob on from new

David at over 4k i want a matching stem and seat post as ive got to live with the bike forever or my mrs will castrate me its gotta be bob on from new

❓

Buy several cheap stems. Try them, decide on which length you prefer, buy a matching seatpost stem in that length. Sell the remaining stems on ebay if you can be arsed.

Id rather drive up tbh. Cheers all

Buy several cheap stems

This – unless you ride Giant, then they aren’t cheap. And I have a spare 100mm because I thought the geometry was the same on my new bike as my old (it isn’t despite the chart).

I keep a set of stems from 60 – 120 mm for fitting (including at least one “half” size). They definitely don’t match! It is surprising how much difference one cm can make when you are on the drops.

Having re-read your post, you have reduced the drop by 6 cm, which is a huge difference! The reach will reduce by 60*Tan(18) = 18-20 mm (72-73 degree head angle). You may need a 2cm increase in stem. My best bike has a 120 mm stem, but a drop of 70 mm. I can ride on the drops all day and prefer the position to the hoods (which should “feel” a bit too high).

Use a sheet of A3 graph paper and a ruler, you’ll then enter into proper bike geek territory.

Im already a bike geometry geek lol i may just say send you standard setback post and 110mm stem and sort it out from there be bloody easier 😉

firestarter : check out my link above (if you haven’t already) , i used it all the time in the shop for showing customers how their position would change, and it’s also helped me out for stem choices.

Some good advice already so far.

The main point to finding as frame that fits is that your saddle should be a constant not a variable. If you can get that settled then everything can be worked out by stack and reach (horizontal and vertical distances relative to the BB).

This is by the the best stack and reach caclulator I have found. Scroll to the right and use the section titled “CALCULATE BASED ON PUBLISHED STACK AND REACH”. It is quite nice that is also account for different stem lengths, angles, spacers and frame geometry so you play around with it to see the effect of different stem lengths and bar heights.

That should get you pretty close and then having a selection of stems around this will get you perfect 😀

That is very clever dan. It shows i had some numbers mixed up my roadbike had a drop of 90mm and saddle to bar 505 so i thought that same reach with less drop would be longer but i set up my cx thinking it was shorter as it measured 485mm saddle to bar but with less drop.

But after using the calculator i found why they felt similar as reach was 0.3mm difference between the two. Explains why they felt the same

So actual bb to ht reach is sound on new bike with 90mm stem but seat is slacker so will be longer aaahhhhh bloody bikes lol

You’re thinking about it too much. A seven hour drive won’t tell you much either. You need to ride it on the road and experiment.

So actual bb to ht reach is sound on new bike with 90mm stem but seat is slacker so will be longer aaahhhhh bloody bikes lol

Nope, no problem here. You seat should be the same place relative to the BB on all bikes. The slacker STA just means that you will need to fit the saddle further forwards on the rails in same seatpost or even try and inline rather than setback post. This is the beauty of sizing bike by stack and reach- it is independant of the sadlle or STA. Seat Tube Angle, seatpost, saddle… it doesn’t matter- these shouldn’t be moved from the optimal position to change the reach (for better or for worse!).

Nope, no problem here. You seat should be the same place relative to the BB on all bikes. The slacker STA just means that you will need to fit the saddle further forwards on the rails in same seatpost or even try and inline rather than setback post. This is the beauty of sizing bike by stack and reach- it is independant of the sadlle or STA. Seat Tube Angle, seatpost, saddle… it doesn’t matter- these shouldn’t be moved from the optimal position to change the reach (for better or for worse!).

That’s nonsense. Saddle position relative to the BB is not a constant; it should be set to achieve a comfortable/balanced position for each individual bike.

Saddle nose is a constant 5 cm behind the BB on all my bikes. Height is a constant 74 cm too. If you are riding a TT bike or unbothered by the UCI, or are of a small stature, the saddle can be further forward (and should be raised slightly) to rotate the rider. But generally, I fit constant BB to saddle and determine weight taken through the core/legs accordingly as a measure of fit.

you need one of these,

Indeed rob. As an example reach on my cx and road bike were the same but road bike had saddle on center of rails and cx had to be pushed forward as slacker st put saddle further back

By my basic maths 1deg at my saddle height is about 9mm further back

So me thinks inline post and 90mm stem will be slightly longer but will do 🙂

That’s nonsense. Saddle position relative to the BB is not a constant; it should be set to achieve a comfortable/balanced position for each individual bike.

No, generally speaking…..

Saddle position relative to the BB is not a constant; it should be set to achieve a comfortable/balanced efficient position for each individual bike person.

It is up to you to select a frame and frame size that you think offers balanced handling for the position your contact points should ideally be located in. There isn’t any reason for the saddle to BB relationship to vary by bike unless the bike is perhaps more gravity orientated and then saddle position becomes more about allowing the best control rather than optimal pedaling mechanics. We are talking about road and touring bikes though so there isn’t anything like that going to be happening for the OP. A decent pedaling position (optimal lower limb biomechanics/ saddle position relative to BB) is a decent pedaling position, why would you want to change it from bike to bike? Just because the OP’s new bike is a tourer doesn’t necessarily mean it has to have extreme changes and go from a nice road position to a horrible sit up and beg type thing. I’d agree in that instance then the saddle to BB relationship would be off but then then whole cycling position would be rubbish anyway so why bother with anything to do with fit. A small raise of the bars, change of stem to adjust reach accordingly and perhaps slight tilt of the saddle should be the most needed.

Edit: You might set up a TT or track bike slightly differently to the road bike but that is more because you want to shift the mechanics towards shorter duration power/ aero rather than considering comfort/ long term performance so much. The same isn’t really true going from one road bike to another or road to tourer IMO.

Alright then, here’s a touring bike

here’s a road bike

and you reckon the saddle needs to be in the same spot on each, regardless of any of the other contact points, so you can achieve “optimal lower limb biomechanics” ?????

Yet for something like this

the optimal lower limb biomechanics rule doesn’t apply?

Saddle position relative to the BB is not a constant; it should be set to achieve a comfortable/balanced position for each individual bike

Correct, imo. It’s about how you fit to a bike and it’s a variable.

It occured to me that the same measurement but with only a 30mm saddle to bar drop will actually feel shorter and requires a longer distance for the same feel.

I think what’s tricky here is the aim of ‘the same feel’. It’s a different bike for a different use so unless you’ve ridden your road bike for tour-like distances/durations over a few days the fit of the road bike isn’t a lot of use as a reference – could work fine though, they do for some of us. Depends on what you call touring. I’ve got drop-bar road and tour-type bikes with very similar (within 10mm) reach from saddle-to-bar but different seat angles and saddle-bar drops, both feel good for intended use. There’s no real need to keep one measurement constant (saddle height aside), the way the reach worked out on those 2 bikes was simply where it ended up rather than an aim.