Fat Bike Frame for BBSHD & 5" Tyres

[namastebuzz]

Ok so I'm helping my little bro with his Fat Bike build.

The need was to pedal in to the snow covered Scottish hills in winter to carry out wildlife photography. The idea was to build an e-fatbike to get him and his gear up there.

He started with the tyres - Vee Tyre Snowshoe 2XL 5.05". Then picked up a Mastodon fork, Kona Wo fatbike and Bafang BBSHD modified 2700w version with a monster 52V 72Ah battery from Electron Cycles.

All sounds good so far (although I would've started with a frame first and worked forward - not with tyres and worked backwards).

So......the issue is the motor casing fouls on the chainstays. There's about a 13mm gap. The Bafang kit is the 100mm one. I realise going for the 120mm version would be one answer but what I'm asking is - is there a FB frame out there that could take the 100mm Bafang motor and accommodate 5" tyres without fouling on the motor?

Any suggestions gratefully accepted. I'd happily consider a custom built frame too - if any one in the UK would do one.

[73Eldo]

The issue is obviously they have no choice other than to kick out the chain stay very quickly to clear those huge tires. You would have to look for a frame that had longer chainstays which I don't think is super common geometry for a fat type bike unless it was more of a cargo style that is crazy long like a Surly Big Fat Dummy. Its hard to tell with all the angles and curves in the photo. How is the chain line with it sitting in that position? Is that a Lekkie 42? If the chain line works just getting the 120 seems like it would be the best move. If the chain line isn't good then you have to find a longer bike.

[namastebuzz]

Thanks 73Eldo

There's a Lekkie 36T on there in one pic and we also have a Bafang 46T.

The chain line isn't great either way but worse with the Lekkie. I'm happy to look at cargo bikes too.

The Bafang unit will need to get sent back for an exchange obviously if we go down the 120mm route.

I looked at the Salsa Blackborow but the 5" tyres won't fit.

[AZguy]

I've got a frame with 197mm dropouts (takes 5" tires) and I did have to shim a few mm - it was nowhere near as much and I mounted a 100mm BBSHD. There was enough threads for the "nut" but not the second ring, but it's been fine after >12,000km

I'd likely just see if you could trade for the 120mm though since you are already that far

YMMV

[namastebuzz]

Thanks AZ

Yeah sending it back may be the option but even the 120mm isn't the greatest fit.

I've discovered the Surly Big Fat Dummy would be the perfect frame for the job but Surly don't make 'em anymore!

Can't find any in the UK (Large) for sale. I've found some in Indonesia but shipping is a killer. If anyone knows of any frames in the US anywhere - please let me know......

[AZguy]

Everything here is in silly short supply and long waits

The 120mmm may be better than you think

[73Eldo]

I think pretty much every ring smaller than a 40 has about a 9mm offset. The stock 46 is 19mm which is about the seam in the gear case. Lekkie 42 is about the same. Lekkie 40 has some sort of spacer hub that can give it 3 different offsets, one of which is in that 19mm range and another in the 24mm range. Note that the Lekkie 40 supposedly requires their new gear cover for added clearance. Luna has their Eclipse line which smallest is a 42 that is about 25mm. 25 pretty much darn near has the chain rubbing on the controller housing. With any of these you still have to have the teeth clear the curve in the chainstay which may also be a problem for many fat bikes.

I knew that Surly barely made any 2021 models but I didn't know that they apparently discontinued several models including the BFD. I thought that was a reasonably popular model for them and it was always hard to find. Quick search I just did there are very few to none here in the USA and I even checked a few local shops that are really close to Surly HQ and tend to have more Surly stuff than other shops and they hardly have anything either. Word on the streets here (home of Surly) is that their parent company went into full on panic layoff and cancel orders mode in March 2020. I think the parent company is fine since they are a major player in world bike parts distribution but all their brands like Salsa and Surly seemed to have took a pretty big hit. Only thing that may save them is all the bike brands have took a hit so maybe they will come back and no one will really notice.

[namastebuzz]

Thanks guys.

Very helpful.

I'll let you know how we get on. The BBSHD was customised to order so will have to investigate their return\swap procedure although they've been super helpful so far.

With hindsight, the Big Fat Dummy would've been the perfect bike for the project but if we can't get one then we can't get one.....

[AZguy]

if only "electrically" customized (i.e. different firmware parameters or even firmware) that's very easy to do so shouoldn't be a big deal, maybe some restocking charge... if "mechanically" customized (e.g. peek/steel primary gear, etc.) that's a way different animal

[calfee20]

Thanks guys.

Very helpful.

I'll let you know how we get on. The BBSHD was customised to order so will have to investigate their return\swap procedure although they've been super helpful so far.

With hindsight, the Big Fat Dummy would've been the perfect bike for the project but if we can't get one then we can't get one.....

What if you cut the BB on the left hand side and then get an offset crank arm for spacing. Since I am going savage here you could also dimple the right chain stay and gain a few more mm.

You might be thinking that if you do that you can never go back but believe me you will never go back anyway.

[Voodoo1]

I wemt through this on my Ice Cream Truck. I also wanted the widest tire clearance.

Even though the bottom bracket is 100mm I had to use the 120mm bbshd because of the chain stays. Then I had to use a lot of spacers for the bottom bracket and several for the offset chainring (luna eclipse 42t).