Converting a hybrid bike to tourer/trail bike - bike geometry

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Converting a hybrid bike to tourer/trail bike - bike geometry
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flag Rodwelljason
Posted: Apr 7, 2021 at 6:00 Quote
Ok so my bike is a carrera crossfire 3 hybrid. I have swapped out the crappy 700c wheels for some entry level 27.5 and upgraded the groupset but at the moment it's a mis match of parts. I'm about to upgrade almost everything. I quite like the handling at the moment. Smaller wheels have made the handling quicker, and acceleration but trade off is it has a lower top speed.

I use my bike for long distance cycling over predominantly off road terain, mainly cycle routes with a lot of road sections. I live in a very hilly part of the UK. That will always be my bikes main use but I would like the ability to go down a technical single track or mountain path at speed and with confidence. I carry a lot of stuff at times but I only use a rear pannier not front

Ok so I have to be careful because of a lower bb height with smaller wheels. I want to raise that. I currently have a 44mm semi integrated 1 1/8 headset, which I can replace for an external 1.5 lower Cup and fit a tapered fork. I'm looking at a set of rockshox pike ultimate rc2 27.5 but what I am trying to work out is what travel I should have and the offset. The pike comes with 120-160 mm travel adjustable by replacing the air spring with one of a different length and 37mm or 41mm offset. I should also mention I have a medium frame 19 inch but I'm 6 ft tall so I have a raiser bar stem and a very long seat post I'm also on the heavier side.

So the cup change will maybe add 10mm. The original forks are suntour nrx 85mm 700c. I can't find comparison lengths for the pike.

This is what I figure, the pike is a 27.5 fork so the stanchions will be shorter. Adding the extra cup with smaller wheel size but 120mm travel compared to 85 will kind of even everything out and won't change the geometry very much at all maybe by up to a degree off head tube angle and on seat tube angle. And I would favour 37mm offset to keep the steering quicker.

Though I am considering 140mm for better trail performance, to raise the bottom bracket height a little and give it more of trail bike feel.

I use a suntour suspension seat post which has has a parallelogram travel so the seats travel moves laterally backwards and down and may put my centre of gravity further back on bumps. I dont find myself on technical trails often enough to warrant a dropper seatpost over comfort on a bumpy 100 mile ride. But should I need to, can always just lower it as required.

I know I am going to get a hundred replies saying just buy a mountain bike.

The parts I am getting will be fairly high spec. 4 pot brakes, a 3 x 11 drive train with a mixture of xt/xtr parts. Hope pro 4 wheels. I'm planning schwalbe smart sam tyres. A few knobbly bits to cope with the off road and single track but a cross country tyre and decent performance on road too.

I may get a mountain bike frame in the future but for now I'm working on parts that I can put on a mountain bike or tourer in the future. I couldn't in a million years afford a bike with the spec I will have all in one go.

So please don't comment saying scrap it and get something more relevant because a pure mtb isn't more relevant. I'm not a professional trail rider. I just want the ability to have more fun off road. Also please don't advice me to get a 1x drive train. It will never have the range for my needs on this bike.

Me being taller on a medium frame, with more travel is inevitable going to centre my weight more over the back wheel. So would a 41mm offset on forks with 140mm travel help lengthen the wheelbase while making it more planted on hills? Should I stick to 120mm and if so 37 or 41 offset.

In stock setup the head angle is 69.5 degrees and effective seat angle is 74 degrees. The frame is aluminium and seems fairly sturdy. I'm pretty sure it will be up to the new geometry and riding I want to use it for.

The bike was second hand originally so don't need to worry about voiding warranty, ther isn't any.

Again please keep in mind the main use is predominantly an off road tourer that will sometimes find its self on tarmac. This bike is tailored to my needs and I bet it won't be for everyone.

I may get it in 120mm, and if find myself wanting more travel and feel the geometry can handle it try out the 140mm. Could even keep it as 120 for main use and should I ever find myself in a bike park fit 140mm spring.

Any constructive advice would be greatly appreciated!
flag fourfourone
Posted: Apr 7, 2021 at 8:30 Quote
buy a new bike. That frame is not designed to handle any sorts of off road riding. Take the money you are going to waste on it and buy a proper bike. You are asking for trouble slackening out a cheap hybrid frame.
flag demo8dave
O+
Posted: Apr 7, 2021 at 8:32 Quote
This isn't just a dismissive comment I'm throwing at you but I really would look at buying a bike for you intended purpose.
All that money on a pike ultimate, 4 pot brakes, hope wheelset and it's still bolted to a budget hybrid frame that isn't meant or built for riding single track
Every change you make at the front yet trying to achieve a higher bottom bracket is then going to change your seat tube angle and this will most likely be a negative change. You'll be changing the angles by about 3deg.
I get get you might be trying to upgrade slowly but it's really going to be a Frankenstein bike without any good attributes. I do feel like this could be a post trolling but if it isn't then please cut your losses and start afresh
flag HaggeredShins
Posted: Apr 7, 2021 at 8:36 Quote
demo8dave wrote:
All that money on a pike ultimate, 4 pot brakes, hope wheelset and it's still bolted to a budget hybrid frame that isn't meant or built for riding single track

+1. Too many compromises, you're overthinking this one.

It honestly sounds like you need a gravel or adventure bike. You can buy/build some pretty stout flat bar grinders these days that are great on trail, which was one of my recent projects as an example. When it comes to geo, comfort and efficiency, you can make a great trail capable bike out of a gravel grinder but you won't be as successful building a road bike out of an XC whip... keep that in mind.
flag nematon785
Posted: Apr 7, 2021 at 8:58 Quote
People can pound single track on old roadbike frames with the addition of cyclocross tires, therefore what you want to do can be done. I have never heard of retrofitting a tapered fork to a straight headtube, but that does not mean it is impossible. My primary concern would be failure of the frame at the headtube with additional leverage from the fork it is apparently not designed for. Also good offroad tires can improve your trail riding dramatically, but you may be limited by clearance at the rear triangle.

I have ridden trail on bikes not designed for it for many years, including ridgid townie bought for 20 dollars of craigslist and roadbikes with cyclocross tires stuffed in place.

I will point out in my experience this has developed bad riding habits that are very challenging to break. Specifically riding behind the seat on descents, poor cornering body position, excessive body movements and generally uncentered stance to avoid crashing.

Line choice becomes very micro and fussy. Every little thing is an attention getter and small trail features are a very big deal. This does not translate well when I ride modern mountain bikes.

It can be done. Just be gentle with your bike, pick the smoothest line, walk rough sections, and slowing down is a great way to avoid crashing...jumping or bike park riding will very likely result in spectacular frame failure and major medical.
flag Rodwelljason
Posted: Apr 7, 2021 at 9:36 Quote
Thanks for the replies so far. Look this isn't necessarily the finished product...its what I will have for now. I've worried about the potential for snapping the frame which would be the main deterrent against 140mm travel...120 wouldn't effect it that much at all and be very doable. I like my bike for touring. But I need parts to better cope with the loads I carry. For example the pro 4 hubs so I'm not replacing a freehub every 6 months. Brakes because I travel over mountenous terrain with a lot of weight and I've had some close calls because of inadequate brakes...those needs will be present whatever bike I use so the parts are fairly important. I don't want to slamm my bike into every corner on a steep downhill track. And it maybe that when I've got the parts a change of geometry could be in order to sort stuff out. But I still need those parts and can't afford them pre supplied on a bike. It's a very serious question. It is going to be tested because I can't do it any other way. And a mtb frame would lack many of the needs I have for touring which is why I said pls don't just suggest a mtb frame. What I want to know is the effects of offset and the best way to balance the handling given my geometry. People put 120 travel on hybrid bikes meant for 65/75mm all the time and have no noticeable changes. And take it down a single track. Again it's an off road tourer.
flag fourfourone
Posted: Apr 7, 2021 at 9:41 Quote
I have never seen a road hybrid bike out on our local trails. It seems like you are basing all your decision on assumptions and not facts. That frame is made for on road use/light gravel only. not only are you wasting money, you are putting yourself in danger.
flag HaggeredShins
Posted: Apr 7, 2021 at 9:49 Quote
You need to make measurements to understand the impact to geo. You can find the axle to crown for the Pike in Srams product specs. You then need to figure out what the axle to crown at 75mm travel is for your current fork (measure it). Then you need to understand the impact of stack height of the lower conversion cup needed to accommodate a tapered steerer in a 1 1/8 head tube. To preserve your geo, I imagine you'll wind up again with less than 80mm of travel on the 650b Pike due to the headset, which will likely compromise damper & spring performance and will require a custom airshaft or a ton of spacers to reduce correctly.

A couple points of constructive criticism:
1. Offset has f*ck all to do with anything in this situation--you need to be far more worried about a2c
2. The 650b Sid is the fork you're looking for, not the Pike
3. You do not need a top shelf fork for 'testing' this. The Ultimate will be completely lost on what you're trying to do. You could spend hundreds instead of thousands doing a good job with your goals here.
flag Rodwelljason
Posted: Apr 7, 2021 at 10:00 Quote
All cards on the table, I love the look of the pike ultimate and I was looking for something with thicker stations than most 120mm xc forks. Also want parts that should I chose to get an all mtb or trail bike...i could just get a frame and put the parts on and change travel ect for the new frame. I want the parts to be future proof and an investment. The pike is the go to trail fork, but comes in 120mm.

Also I don't want to preserve the geometry. I want to lift to bottom bracket a little and slacken the head tube angle a little to give a little better off road geometry. Which I think a 120mm travel fork will do. I've certainly seen few YouTube videos where they upgrade from the stock coil fork to suntour epixion 100 and 120mm forks and hardly notice anything in handling other than better performing suspension. Im gonna try get all the measurements and see just how much difference there is.
flag HaggeredShins
Posted: Apr 7, 2021 at 11:04 Quote
Nothing wrong with doing things for looks, but this is a lot less of a watertight idea than you likely think. You're taking a top of the line AM fork, halving its intended travel, and using it for something it was never designed for. Not only will you totally compromise the performance of the fork, but your geo will suffer and the bike will be much heavier than it needs to be. The Sid or 32 are light, far stiffer than this bike needs, and entirely capable of operating as low as 50mm travel--even better yet, older variants of each have a 1-1/8 steerer and are easier to modify.

Hubs, brakes, 650b are all great idea for usability and reliability but trying to put a modern Pike on a generic hybrid bike (less one that can't accommodate a tapered steerer, requiring a huge a2c increase) is only slightly less ridiculous than putting a Boxxer on an XC bike.
flag lookseasyfromhere
Posted: Apr 7, 2021 at 12:05 Quote
Rodwelljason wrote:
And a mtb frame would lack many of the needs I have for touring
What are these "needs" that a mtb frame would be lacking?
flag Rodwelljason
Posted: Apr 7, 2021 at 12:11 Quote
lookseasyfromhere wrote:
Rodwelljason wrote:
And a mtb frame would lack many of the needs I have for touring
What are these "needs" that a mtb frame would be lacking?
The need for rack mounts, a place to put external bags, a tripple speed crank.
flag Rodwelljason
Posted: Apr 7, 2021 at 12:13 Quote
No the pike comes as a 120mm option, it is sold that way.
flag HaggeredShins
Posted: Apr 7, 2021 at 12:21 Quote
Rodwelljason wrote:
No the pike comes as a 120mm option, it is sold that way.

It doesn't matter what configurations its sold in, it matters what it needs to be set at for your application.

IIRC the 27.5 Pike is around 515mm a2c at 120mm travel. I don't know what fork you have but its likely the Suntour NVX, which most hybrids have, and has about 490 a2c. You're probably going from a ZS to EC lower cup for your 44mm ht, which means a gain of anywhere from 10-20mm lower stack depending on brand. Quick mental math says you'll be able to get away with at most 90mm travel on the Pike with anything near your current geo.

+30mm travel over your current geometry will ride like absolute, unbridled dog shit and running the pike -30mm under its minimum travel spec will perform similarly. You have too many extreme compromises in this config. You don't have to hear it, but this is the case.
flag nematon785
Posted: Apr 7, 2021 at 12:35 Quote
A bikepacking rig may be right up your alley. I'd take a stock ridgid surley or Kona Unit over the fork/wheels/brakes upgrade on the hybrid all day long. These are mountain frames made for exactly what you are doing. Bonus is room for tires made for the job. And they rated to take a suspension fork. Fenders, racks, bags all no sweat.

If you are riding substandard tires, all the brake power in the world cannot help you.
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