if you were to take the plus tyres and wheels off a plus bike, it would drop the bike sown a inch or so, nearer to the ground.

would this change the handling of the bike much ?

someone i spoke to told me the bike was designed to be used with plus wheels/tyres.
i think the bike is just a mtb frame with wider forks and a tweaked back end for the rear tyre.

anyone make it a bit clearer ?

I think it depends on the actual bike Tony. many frames can accommodate 29" or B+ ... happy coincidence that they're basically the same diameter?

I'd imagine and James or Steven would be the mean for this - that a 29+ would be a different matter and largely designed around the wheels / tyres.

First thing you'd notice might be clonking your pedals on rough ground. Dunno if you're referring to your ECR but isn't that the issue with them? Low BB with plus tyres translates to a really low BB with normal tyres?

yes it is the ecr.
just measured the bb height. it is the same as my disc trucker. never noticed the low bb thing, even offroad.

There would be a miniscule change to the handling. Wheelbase is the same. Head angle is the same. You've just dropped the BB a little.

My Pact has both B+ and 29er wheels (currently running 2.1" tyres). I don't notice the small difference in BB height when riding (I think it's about 8mm). The B+ wheels are a bit more forgiving on rough terrain, the 29er slightly faster rolling.

perfect then, that is what i wanted to hear. cheers colin.

Surly talk about this here:

https://surlybikes.com/blog/everything_comes_round

Hang on Tony - Colin (as I was) is comparing 29" to B+ but from what I can see, there'll likely be more of a difference between 29" and 29+ as generally, the diameters are noticeably different.

Bearbonesnorm wrote: ↑Tue Nov 24, 2020 4:11 pm Hang on Tony - Colin (as I was) is comparing 29" to B+ but from what I can see, there'll likely be more of a difference between 29" and 29+ as generally, the diameters are noticeably different.

I had an ECR for a while, it’s got a low bottom bracket, very much designed as a 29+
With ‘normal’ 29” tyres it’s like a dog with worms.

i have fitted some schwalbe marathon mondial 28 x 2 tyre to it.
just been for a mile spin, and it feels fine. i wont be riding it offroad much. well not proper offroad.

There's a limit to BB clearance in the EN standards, it's based on lean angle so tyre/wheel OD and crank and pedal specs affect it. Many bikes will pass the standard with plenty of space since you want more clearance to pedal off-road, so on-road with narrower tyres is fine - beneficial even. I've ridden a fat tyred road bike with a BB too low to pass testing and it was great as long as you didn't pedal through corners (why would you?).

cheers jameso. i will report back once i ride it for some distance.

Asking the same question in reverse (I think) - if a frame has been designed for 29" tyres but the buyer wanted to put 29+ on it should the geo be adjusted accordingly, ie. the BB drop increased or something?

they would not fit , chainstays on a + bike are obvously pretty wide ] so I would not worry about it
With 19 I would assume they would also be too short
If it worked BB is raised No idea re head angle and other stuff

My solution to all this is to have a fat bike and just stick lots of different wheels n tyres on it. Only thing Ive not tried is 29+ which may be pushing it. Or not.

Asking the same question in reverse (I think) - if a frame has been designed for 29" tyres but the buyer wanted to put 29+ on it should the geo be adjusted accordingly, ie. the BB drop increased or something?

This is where an EBB is good, +/7mm BB height. 14mm BB height adjustment is close to the axle height change in going from one realistic extreme of tyre size in a frame to the other.

Lazarus wrote: ↑Tue Nov 24, 2020 5:32 pm they would not fit , chainstays on a + bike are obvously pretty wide ] so I would not worry about it
With 19 I would assume they would also be too short
If it worked BB is raised No idea re head angle and other stuff

in this (purely hypothetical) example:

• a customer has approached a designer/builder about a bespoke 29+ frame
• the designer asks some questions, takes a deposit, and produces a design
• the design is sent to the customer for comment
• the customer's comment is "you've used the wrong wheel diameter m8"
• the designer apologises and revises his drawing to incorporate longer chainstays and more clearance
• the customer doesn't consider that BB height/drop maybe should also have been amended and approves the drawing
• the frame is lovingly handbuilt to the approved drawing and should be with the customer imminently

Has the customer made an oversight in this instance? Is the designer a turnip?

jameso wrote: ↑Tue Nov 24, 2020 6:24 pm
This is where an EBB is good, +/7mm BB height. 14mm BB height adjustment is close to the axle height change in going from one realistic extreme of tyre size in a frame to the other.

Hadn't considered this.

My solution to all this is to have a fat bike and just stick lots of different wheels n tyres on it. Only thing Ive not tried is 29+ which may be pushing it. Or not.

that is what i am hopefully doing with my ecr.
1 set with 29 x 3 and 1 set with 29 x 2 touring tyres.

in this (purely hypothetical) example:

In that case the laws of capitalism dictate that the customer is never wrong [always right] so its the frame builders fault.

Pretty sure its technically the customers as they approved but it is certainly an oversight on both sides -one you would NOT expect the expert framebuilder to make.

I hope I don't regret saying this

in this (purely hypothetical) example:

...the designer is indeed a turnip*, as BB drop is as much a part of this as chainstay length. You'd start with wheel OD as a driver of the design, also the forks. If you go to a builder who is also a designer then they shouldn't make a mistake like that (ie imho builder and designer are not the same thing, some do both very well but not all). The customer is buying build and design skills so shouldn't have to take responsibility for saying that all aspects of geometry are correct?

*or may be not, if they chose a BB drop that worked for 29+ in the first place

An ECR with normal 29er tyres will still have a higher BB than a jones with plus tyres and the EBB in the lowest position. You'll be fine. Note that a reduction in wheel dia results in a reduction in trail so it will handle (slightly) differently. You may not notice it unless you ride both back to back.....

jameso wrote: ↑Tue Nov 24, 2020 8:09 pm ...the designer is indeed a turnip*

This is my take on it too. It's made worse by the fact the customer only spotted the error when he asked for the CAD file and interrogated it at work. It wouldn't have been picked up by someone who didn't have that capability - they'd have found out 3 months down the line when the frame was delivered and they tried to get their £1500 carbon wheelset to fit

*or may be not, if they chose a BB drop that worked for 29+ in the first place

alas they did not - they used the one from the customer's current 29er frame after the customer had described how much they like the way it handles. It's 51mm. Maybe it will work. Here's hoping!

The effect of this is basically that centre of gravity is raised by 17mm, BB clearance is increased and standover clearance decreased right? The centre of gravity bit can be addressed by an EBB as you've helpfully pointed out. Anything else that would be an issue you think?

Very much appreciate your input btw.

I think the ECR is a great bike, it’s 80mm BB drop and long chain stays combined with the gyroscope effect of the big old wagon wheels make it super stable. At speed I found it needed some proper body English, much like riding some motorbikes.
That’s not such a bad thing, it makes it easy work loaded.
But as much as I loved the ECR I found the 3” tyres very slow on the road, I’ll admit I never tried 2.3” tyres as I felt that it would be just too low off road, I’m looking at my Fargo with its 70mm drop, I run 170mm cranks due to shortarseness and I really not want my pedals 15mm closer to the ground which I’m s where the ECR would be shod with 2.3s.
Of course on the road you don’t have the clearance issues.

Having embraced my short legs I’d quite like to try some 165mm cranks and perhaps a 5mm lower bb, an eccentric BB and adjustable dropout lengths would be fun. Compromise is part of life, as they say your mileage may vary.

Incidentally WTB rangers (29x3) roll incredibly well on hard surfaces. They grip on the dirt pretty good too....